Solve Problems Using Proportional Relationships

What is a proportion?

An equation that states that two ratios are equal.

What are cross products?

A method used to determine if ratios are equal.

Strategy 1 for solving proportions

Look for equivalent fractions.

Strategy 2 for solving proportions

Test using cross products.

When will a ratio remain proportional?

If the numerator and denominator are multiplied or divided by the same number.

Example 1: 425 miles/25 gallons compared to 7 miles/5 gallons. What is the equivalent fraction?

425/25 = 85/5, so they are proportional.

Example 2: Use cross products for 425/25 and 85/5. What do you get?

425 × 5 = 2125 and 25 × 85 = 2125, so they are proportional.

Quick tip for proportional relationships

If cross products are equal, the ratios are proportional.